Research On Visible Light Communication Based On Constellation Probabilistic Shaping

Visible light communication(VLC)technology based on white light emitting diode(LED)is a new high-speed wireless communication technology.It is rich in spectrum resources and can be used without application,suitable for various access scenarios.The VLC with the advtanges of no electromagnetic interference,green and environment-friendly operation and high security is able to realize the lighting and communication simultaneously at low prices.Therefore,it has attracted more and more research attention.However,due to the limited modulation bandwidth of white LED with a typical value of serval MHz,the achievable information rate(AIR)of VLC system is severely constrained.Recently,lots of schemes including equalization techinque,blue filter to improve modulation bandwidth,or high-order modulation formats such as pulse amplitude modulation(PAM)and orthogonal frequency division multiplexing(OFDM)have been reported to improve the AIR.However,the AIR is still far away from its Shannon capacity.The main research outcomes of the thesis include:(1)We establish the VLC model,and investigate the channel response by the combined deterministic and modified Monte Carlo(CDMMC)method.Under the condition of a single transmitter and a single receiver within a room size of 5m×5m×3m,we verify that the VLC system is a typical bandwidth-constraint transmision system.Moreover,the effect of limited bandwidth can be fully utilized by multi-carrier modulation in order to obain a higher AIR,especially DC-biased optical orthogonal frequency division multiplexing(DCO-OFDM).(2)We introduce the metrics of AIR arising in the coded modulation(CM)system including mutual information(MI),generalized mutual information(GMI),and normalized GMI(NGMI)as an error measurement of forward error correction(FEC)overhead,in order to clearly explain the principle of probabilistic shaping(PS)techinique.With the help of the Monte Carlo simulation,we numerically present the improvement of the GMI for PS-M-ary quadrature amplitude modulation(PS-M-QAM)in comparision with the uniformly distributed M-QAM under the condition of optimal probability distribution,especially the potential capability to approach the Shannon capacity.(3)We propose a scheme combining the multi-carrier modulation and PS technology,which is called as the entropy-loading scheme.For each subcarrier,the best PS-M-QAM is determined by its signal to nosie ratio(SNR),so that the AIR of the VLC is approaching the Shannon capacity.We verify that,the proposed entropy-loading scheme is better than the traditional bit-loading scheme in different scenarios,with numberical simulation and experimental demonstration.In the verification experiment,the VLC system uses a phosphor-LED with a bandwidth of about 45-MHZ,the transmission distance in free space is 1-m,and the entropy-loading scheme achieves AIR of 204.1-Mb/s,which is 26.8% higher than the conventional bit-loading scheme.